Infanticide, or a member of a population (usually a male) killing the young of another female, has been documented in some species. The reasons behind this behavior can vary, but it is often thought to increase the males' chance of mating with the female (by making her go back into estrous) and siring offspring, thus increasing his fitness by increasing his genes in the population. This behavior has only been documented (or suggested) in a few cetacean species. This low occurrence may be because it is rare in these species, or because of the difficulty in observing cetaceans at sea, both in terms of time on the water, and being able to see what is happening below the surface. This paper documents the rare event where researchers observed the killing of a killer whale calf, only a few days old, by a mature adult male and his mother (who was no longer reproductively active). Join us as we discuss what happened, the possible reasons behind the behavior and why this type of behavior is important to understand.